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Recently we are facing a severe problem of frequent RGC trip in our Hydrocraker plant. Till now RGC tripped 10 times in last 3months. Now the problem is that in all these trips not a single trip logic actuated, but only the alarm received as compressor trip from governor. So we are clueless. We have HP steam driven RGC. At present we are bypassing trip lever &mechanical overspeed suspecting problem in that part.It was also observed that most of the trip occured at when governor speed incresed to 11,500 rpm.In last few occasion of trip it was also observed that turbine outboard bearing Outlet Lube oil temperature suddenly started shoot up just before RGC trip. After byassing the trip lever assembly RGC was not tripped till now,but as trubine outlet bearing lube oil temperature increased at speed 11,500,we have reduce the rpm to 11,00 and thus we are not able to run Hydrocraker unit in full capacity.From process point of view, all parameters are within normal operational range like previous normal RGC running condition.Can any one give any idea what may be the basic problem of frequent RGC trip? Also,will it be safe to run RGC by bypassing trip lever assembly & Mechanical overspeed?
 
Answers
28/06/2016 A: Sarin Reghunath, BPCL - Kochi Refinery, sarinreghunath@gmail.com
Check L.O supply pressure to each thrust and journal bearing.
02/12/2011 A: Bruce Carr, Suncor Inc, matukaze1@hotmail.com
By the sound of it would appear the increase of speed to 11,500 and subsequent increase in flow through the compressor is causing shaft movement that is loading up the thrust bearing of the turbine. If the compressor is equipped with a balance line, has there been any changes to the balance line pressure or flow... excessive clearance of the balance piston labyrinth would mean the axial thrust is not being compensated adequately...
As for bypassing the the trip assembly I didn't think it was possible, unless you are referring to the pressure balancing lever, this is used when the turbine has tripped and allows the trip lever to be reset without having to isolate the compressor... I don't think that will bypass the trip mechanism.. If you have a means to bypass the trip mechanism it is very dangerous to run that way... if you ever have a broken coupling for example the turbine would fly apart in a short time..
29/05/2011 A: jagjit singh, indian oil, singhj5@iocl.co.in
if you are running very close to the overspeed then check your exhaust pressure. if exhaust pressure decreases then the speed of turbine will increase due to speed all the bearing temperature rise.
23/05/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
1) The increase in temperature of the lube oil exiting the turbine is very troubling. WHY does it now show such an increase with modest speed increase?? What has changed to cause this? Has the oil been changed? Is the lube oil filter plugged? Is the lube pump failing. Is it cavitating?
Find the root cause for the lube oil temp rise before the turbine bearing fails. SOMETHING is causing that temp rise, and ALL of the possible causes are predictors of bearing failure and potential catastrophic damage to the turbine.
I suspect lube oil pressure/flow loss is also causing governor instability and causing the trips.
23/05/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
"From process point of view, all parameters are within normal operational range...". Does that include the gas molecular weight? If too low, compared with the data sheet, try increasing the separator temperature or bleeding in some methane at the compressor suction.